Cylinders containing a compressed gas can be found in environments such as manufacturing, research, production or synthesis facilities, hospitals, labs, classrooms, or any environment where a source of the desired gas is not otherwise available. The cylinders have a wide range of sizes and shapes, and are adapted to hold a particular type of gas. Most cylinders are a generally upright container having a flat bottom to allow the cylinder to rest vertically on a level surface. At the top of the cylinder is a port through which the compressed gas leaves the cylinder, typically through a valve installed on the cylinder by the gas supplier, and then through a regulator and/or flow meter installed by the end user and adapted to control the flow of gas from within the cylinder to the application point. Such cylinders are commonly employed to transport calibration gases, for example, to calibrate instruments, air monitors and safety systems at remote locations.
Gas cylinders are transported to an end user by a supplier at a time when the end user desires the gas. There are two types of gas cylinders used for portable and other calibration purposes. A type 1 cylinder is a refillable cylinder, which generally, but not always, provides protection to the valve by means of a metal cylinder cap. Refilling certain type 1 cylinders is typically accomplished through a fill port that must be engaged by a compatible fitting projecting from a supply line. During refilling, the fittings allow gas to flow from an external source through the cylinder valve into the cylinder. These fittings are commonly found on refilling devices that adhere to standardized thread designs that are available to end users to potentially enable the end users to attempt refilling of the cylinders when desired, possibly with an inappropriate gas. Many type 1 cylinders and type 2 cylinders, discussed below, do not have any means at all to prevent unauthorized refill of the cylinders.
A type 2 cylinder is the so-called “disposable” cylinder that generally provides no valve protection, as there is generally no metal cap with a type 2 cylinder. The metal cap, as found in some type 1 cylinders, is designed to protect the cylinder valve from contact with, and damage from, foreign bodies, encountered in a fall, drop or other impact of the cylinder valve during such an accidental event. Typically, gas is delivered to the end user in suitable quantities to satisfy the end user's needs for a period of time. Several gas cylinders are usually stored at the end user's location at any given time to ensure the availability of the gas when it is needed. As the contents of the cylinders are consumed, the pressure gradient between the interior of the cylinder and the ambient environment is no longer large enough to allow a user to withdraw gas from within the cylinder. At such a time, the cylinder's contents become consumed, and the cylinders are returned to storage at the end user's location to await final disposition. A substantial number of end users simply throw away disposable cylinders when the contained gas has been consumed, whether or not the cylinders are properly processed for disposal according to Federal, State and local regulations.
A technician must install the flow meter along with the regulator, which are not typically supplied integral to the cylinder valve by the supplier of the gas cylinders. Thus, a supply of properly functioning regulators and flow meters of varying pressure reducing and flow regulating characteristics must be maintained by the technician, or the technician's employer, to ensure proper delivery of the gas from the cylinder.
After installing the regulator, a technician calibrating an instrument, for example, will supply a quantity of gas having a known concentration, or another known property, from within the cylinder to the instrument, and the response of the instrument monitored. The response of the instrument is observed and compared to the concentrations of gas(es) within the cylinder as listed on the cylinder label. Automatic or manual adjustment of the instrument is made so that these values agree. Great care must be exercised on the part of the technician to prevent the exposed valve, flow meter and regulator from impacting a foreign object. A sufficiently strong impact may shear any of the valve, flow meter or regulator from atop the cylinder, causing a sudden release of the cylinder's contents. Pressurized cylinders having the valve, flow meter or regulator sheared off during a fall or otherwise striking a foreign body, have been known to become dangerous due to the sudden thrust from the pressure release. In such cases, the cylinder can become a projectile.
In type 2, or disposable cylinders, once the cylinders' contents have been consumed, the cylinders are to be properly recycled or discarded. Due to the sometimes potential and actual hazardous nature of the cylinders' contents, recycling the cylinders is problematic, and can cost from hundreds of dollars to thousands of dollars for each cylinder. End users operating on a limited budget may often stockpile many cylinders until an alternative use, or a cheaper avenue of disposal arises. The stockpile of consumed cylinders is often neglected and exposed to the elements, which causes the cylinders to degrade over time. As the cylinders degrade, cracks or leaks may develop and allow residual traces of gas to escape the cylinder into the surrounding environment. Further, consumed cylinders may tip or otherwise be knocked over, once again breaching the integrity of the cylinders, possibly allowing residual traces of gas to escape, as well as producing the projectile effect aforementioned.
To maximize portability, and minimize weight, the type 2 or so-called disposable cylinders have been developed to be discarded upon consumption. These are commonly used to provide a one time supply of gas to an end user who has few alternatives for a portable gas supply other than gas contained within a disposable cylinder. The disposable cylinders are frequently discarded as solid waste when they are consumed. Once again, though, due to the often hazardous nature of the cylinders' contents, facilities that accept consumed cylinders typically charge large disposal fees. Further, discarding the disposable cylinders contributes to the growing accumulation of solid waste at disposal sites. As a result, there is frequent confusion on the part of end users as to how to properly dispose of or recycle “disposable” cylinders when the contents have been fully or partially consumed.
Alternative uses for compressed gas cylinders developed by the end user are often beyond the intended use of the cylinders when they were originally designed. Attempts by the end user to refill a cylinder may subject the cylinder to unsafe high pressures or to hazardous materials for which the cylinder was not designed. A corrosive gas stored in a cylinder designed for an inert gas, for instance, can degrade seals or gaskets of the cylinder and allow the improperly stored gas to escape to the atmosphere. Such a release can cause irreparable damage to the environment, and can be hazardous if inhaled. Refilling of disposable cylinders is prohibited by the United States Department of Transportation and there are heavy fines for offenders as well as potential jail sentences.